HPLC analysis of reduced and oxidized coenzyme Q(10) in human plasma

Background: The percentage of reduced coenzyme Q(10) (CoQ(10)H(2)) in total coenzyme Q(10) (TQ(10)) is decreased in plasma of patients with prematurit y, hyperlipidemia, and liver disease. CoQ(10)H(2) is, however, easily oxidi zed and difficult to measure, and therefore reliable quantification of plas ma CoQ(10)H(2) is of clinical importance. Methods: Venous blood was collected into evacuated tubes containing heparin , which were immediately placed on ice and promptly centrifuged at 4 degree sC. The plasma was harvested and stored in screw-top polypropylene tubes at -80 degreesC until analysis. After extraction with 1-propanol and centrifu gation, the supernatant was injected directly into an HPLC system with coul ometric detection. Results: The in-line reduction procedure permitted transformation of CoQ(10 ) into CoQ(10)H(2) and avoided artifactual oxidation of CoQ(10)H(2). The el ectrochemical reduction yielded 99% CoQ(10)H(2). Only 100 muL of plasma was required to simultaneously measure CoQ(10)H(2) and CoQ(10) over an analyti cal range of 10 mug/L to 4 mg/L. Intra- and interassay CVs for CoQ(10) in h uman plasma were 1.2-4.9% across this range. Analytical recoveries were 95. 8-101.0%. The percentage of CoQ(10)H(2) in TQ(10) was similar to 96% in app arently healthy individuals. The method allowed analysis of up to 40 sample s within an 8-h period. Conclusions: This optimized method for CoQ(10)H(2) analysis provides rapid and precise results with the potential for high throughput. This method is specific and sufficiently sensitive for use in both clinical and research l aboratories. (C) 2001 American Association for Clinical Chemistry.